Study of the Effect of Microstructure Characteristics on Corrosion Resistance of Cold-Rolled Micro-Alloyed Sheet Steels (Hsla) of Strength Classes 340–420 for Automobile Building

The effect of microstructure characteristics and also production regimes on corrosion resistance of cold rolled high-strength low-alloy steels (HSLA) grades 340 and 420 is studied. It is shown that the corrosion resistance of cold rolled HSLA steels of strength class 340 (НС340LA) is determined both by aging processes, developing in overageing sections of continuous annealing units (CAU), and also formationm of a considerable amount of nanosize niobium carbonitride precipitates. For rolled product of strength class 420 (НС420LA) with a higher manganese and niobium content after annealing in a CAU average values of corrosion rate are slower than for rolled steel of lower strength classes. Probably, for this steel the aging process does not significantly affect the corrosion resistance. At the same time, an increase inannealing temperature to 750–762°C leads to an increase in corrosion resistance due to the coagulation of nanosize niobium carbonitride precipitates and a reduction in their amount (≈ 1500 to 600 precipitates/ μm2 or less).